Investigations On Traping And Detraping Dynamics Of Persistent Phosphors

Persistent phosphor is a kind of luminescent material.This kind of material can store energy in the traps distributed below the bottom of the conduction band.For charging the storage phosphors,it typically uses high energy ionizing radiation.This high energy excitation capability has limited the practical applications of persisitent phosphor in various fields.Up-Conversion Charging(UCC)is an effective approach of filling traps using visible or near-infrared light.UCC technology provides an option for charging persisitent phosphor using low-energy excitation light sources.In recent years,investigations on UCC mostly focus on the design of nonlinear up-conversion excitation pathway or the modulation of emission wavelength,lacking of research on traping and detraping daynamic of the persistent phosphors.Prior studies show that the excitation light also empties the traps while filling them.The study of this competition between the filling and emptying of the traps in the excitation process is of great significance both to the fundamental luminescence field and practical applications.In this paper,the nonlinear excitation traping process of UCC is studied by taking LaMgGa₁₁O₁₉:Mn²⁺material as an example.The dynamic rate equation of UCC is developed and extended to the form of single-photon linear excitation trap filling by taking LaMgGa₁₁O₁₉:Ni²⁺material as an example.The specific research contents are as follows:(1)According to the characteristics of up-conversion excitation and optically stimulated emptying,the study develops the UCC dynamics rate equation analyzing the competition between trap filling and emptying.The UCC process of LaMgGa₁₁O₁₉:Mn²⁺material is realized by 450 nm laser and the UCC rate equation is verified by spectroscopic experiments with the matrial.It is shown that the competition between the filling and emptying of the traps becomes more and more intense with the increase of the illumination dose.(2)We further explore the excitation mechanism of UCC in LaMgGa₁₁O₁₉:Mn²⁺and the regulation of its afterglow traps.Experimental result shows that the excitation mechanism is excitation state absorption up-conversion.Based on the UCC dynamic rate equation,a method of regulating the traps by excitation of the same wavelength is designed.If the material is pre-charged,high power excitation light can continue to fill the traps,however low power excitation light will constantly empty the traps.(3)Based on the UCC dynamic rate equation,the dynamic rate equation is extended to the form of single-photon linear excitation.The extended dynamic rate equation extra considers the effect of ambient temperature on trap filling,which complements the UCC dynamic theory.Taking LaMgGa₁₁O₁₉:Ni²⁺material as an example,we experimentally verify the correctness of the extended rate equation using a 266 nm laser.The experimental results are in agreement with the theoretical analysis.It indicates that the competition between trap filling and emptying is related to the illumination dose and illumination time.With the increase of illumination dose and time,the effect of the excitation-light stimulation and the ambient-temperature stimulation become more and more intense,the same with the competition between the filling and emptying of traps.